Sample handling and preparation

1 Sample Preparation and Handling. - There are a wide variety of sampling techniques used for collecting Raman spectra of solid catalyst systems depending on the type of sample and the conditions under which the measurement is to be made. Simple sample holders can be used if the sample is stable under ambient and atmospheric conditions. The sample morphology is not as important in Raman spectroscopy as it is in other types 

As mentioned above, the XPS-experiment is performed in a vaccum of 10 5 torr or better. If solid samples are to be examined, certain requirements concerning the vapour pressure of these compounds have to be met. If the vola- 

On the other hand, with an efficient pumping system spectra of gaseous compounds can be observed, if the technique of differential pumping is employed. Gas spectra 29) normally show excellent resolution and no charging effects. Only water solutions as liquid beams 30) still cause severe instrumental problems and wait for a suitable solution. 

There are numerous ways to prepare a solid sample for XPS-analysis 17K Because of the 360° angle of acceptance, the optimum sample geometry is a cylinder of 11 mm diameter and 2 mm width. However, with a certain loss in sensitivity, flat samples as well as odd shaped samples can be analyzed as well, if they do not exceed the maximum size defined by the vacuum interlock. Sample powders are normally mounted on sticky tape or pressed into a metal grid 17). Excellent results were also obtained by pressing pellets 31) or by subliming the sample directly unto the sample holder. 

Unlike most analytical techniqnes, SIMS generally requires little in the way of sample preparation. Indeed, all that is generally required is  

The sample is Ultra High Vacuum (UHV) compatible, i.e. does not evaporate 

The substrate s surface remains clean before and during analysis 

The substrate s surface is flat and smooth over the area of interest 

Smooth surfaces are required as this reduces topographically induced secondary ion yield variations and is important when HMR in Time-of-FUght instruments using pulsed primary ion beams is required. 

---

Elimination of sample preparation and handling of toxic solvents such as carbon disulphide Absence of solvent simplifies chromatograph Increased sensitivity Sample tubes can be reused ... 

Deviations from Proportionality Summarized. Sample Preparation and Handling... 

Spex CertiPrep Inc., Handbook of Sample Preparation and Handling, Metuchen, NJ (1997), p. 116. 

As for all trace-level analyses, sample preparation and handling are of crucial importance. In addition to all the usual problems of GC-MS, measurements of isotope ratios must ensure that none of these steps introduce any isotope discrimination. Any chemical reactions, including conversion of the organic sample molecules to the simple gases which are those actually analyzed, must be quantitative (100% conversion) to avoid kinetic isotope effects [627]. Until relatively recently, all gas IRMS experiments employed a dual-inlet system to permit switching between sample and standard C02 contained in two bellows containers. The pressures in the two bellows are adjusted to be equal and,... 

Even when hydrolysis and epimerization can be avoided during sample preparation and handling, it is not possible to conclude definitively whether the compounds found in plasma and urine are true metabolites or simply degradation products. Indeed, chemical degradation can also occur within the body since urine and plasma contain a wide variety of potential catalysts, including metal ions, phosphate ions, proteins, and sugars (see Sect. 5.2.6). Whereas the existence of mammalian enzymes that act on penicillins and cephalosporins is considered possible [155], no such mammalian enzyme appears to have been identified to date. 

A large part of the documentation of the laboratory will be of the procedures of the test method and associated sample preparation and handling. However, use of a standard method that is published with sufficient information as to how to carry out the method does not require further documentation. 

Variations in the data that fall outside the experimental allowable limits may be due to factors that originate during sample preparation and handling, such as (1) the sample moisture may not have been in equilibrium with the laboratory atmosphere (2) the sample may have been overdried or under-air-dried (3) excessive dust loss may have occurred during screening due to a loose-fitting... 

Carry out the same procedure for the other starch solutions buffered at different pHs. Use your time wisely all the solutions can be handled simultaneously if you are familiar with the procedure. Slightly stagger the sequential sample withdrawal so that there is enough time for sample preparation and handling. 

It is tempting to draw analogy with the development of other analytical technologies (NMR, FAB-MS) and conclude that protein crystallography will soon leave the incubator of "big machine physics" to become an everyday, routine tool used in the medicinal chemistry laboratory. Hopefully, this chapter has shown some of the subtle complexities of sample preparation and handling, data collection, and refinement, etc. that temper this vision and will likely keep this a specialized field for some time. 

---